There is an inherent danger in connecting the drain lines of equipment and appliances directly to a building's main drain or sewer pipe. This is because the potential of backflow of sewer fluids through the drain lines into the equipment or appliances can contaminate the equipment or, worse, allow entry of the sewer into the public water supply. Such backflow can be caused by an unexpected increase in liquid pressure in the sewer system or an unexpected decrease of the liquid pressure in the drain line. For this reason, many state and local governments have established codes that must be complied with before an equipment drain can be connected to the sewer system. Such codes typically require that an air gap be established between each equipment drain line and the sewer system to prevent backflow. This air gap creates an indirect drain line between the equipment or appliance and the main sewer line. The discharge line must dispose of its liquid waste by discharging into a plumbing fixture which itself is connected to the building drainage system. The plumbing fixture most generally provides an air gap between the equipment or appliance drain line and the drain standpipe, grid or hub which is connected to the building drainage or public sewer system.
The prior art includes devices to provide the needed air gap and/or prevent backflow. Much of the prior art consists of complicated devices employing valves with moving parts, or baffled chambers requiring machined parts. Some simpler air gap devices have entered the field such as the device disclosed in U.S. Pat. No. 5,860,444. These simple devices fail to meet the needs of many supermarkets, vending companies and restaurants, and homeowners, however, who require the ability to discharge multiple lines in a cost and space efficient manner as well as providing flexibility in how the fixture is attached to the building drain system. In addition, these simple devices still require use of a specifically sized device for each drain line.